1. Technical Field
The present invention relates in general to plasma enhanced chemical vapor deposition processes and, in particular, to an improved system, method, and apparatus for depositing a thin film carbon overcoat with a filament that reduces the occurrence of carbon voids on magnetic media disks in hard disk drives.
2. Description of the Related Art
The use of thin film carbon overcoats on magnetic media disks in hard disk drives have several advantages. The overcoats provide corrosion protection, scratch and wear resistance, and a surface to which lubricant film may bond. The rapid increase in magnetic recording areal densities in disk drives has required smaller magnetic spacing between the read/write heads and the disks. In turn, smaller magnetic spacing require an even thinner film overcoat. However, in order for a thin overcoat to maintain sufficient corrosion and mechanical robustness, the density of the carbon overcoat must be increased to compensate for the loss in thickness.
Dense overcoat films may be formed with plasma-enhanced chemical vapor deposition (PECVD). The overcoat is deposited on workpieces from a sputter chamber and is accumulated to form the necessary film thickness after multiple deposition cycles. Unfortunately, PECVD thin film carbon is highly stressed after it is deposited and tends to delaminate from the manufacturing hardware surfaces. The delaminated film produces contamination in the form of undesirable carbon flakes and particles that are unintentionally deposited on the hard disk surfaces. Although the particles can be removed with post-processing manufacturing techniques (e.g., tape cleaning), such techniques indiscriminately also remove the overcoat itself, which leaves small areas on the disk surfaces without overcoat protection. These imperfections in the overcoat are also known as carbon voids. When disk drives are operated in corrosive conditions, such as high temperature, high humidity and repeated condensation cycles, the carbon voids can cause hard disk drive failure.
In the prior art, the filament posts used to support the filament for thin film deposition were observed to be a significant source for generating the unwanted carbon particles and carbon voids. For example, prior art designs for filaments used to deposit PECVD thin film overcoats are disclosed in U.S. Pat. Nos. 6,203,862 and 6,101,972, which are incorporated herein by reference.
In those designs, a tungsten filament 10 (FIG. 1) is used to generate thermal electrons that interact with a gas precursor (e.g., acetylene) to create a plasma. The tungsten filament 10 is mounted between a pair of electrodes 11 (one shown in FIG. 1). A negative potential or bias 17 is typically applied to the filament and filament post. The intent of the bias is to accelerate electrons away from the filament and enhance the ionization of the working gas. An incidental and undesirable effect is the deposition of highly stressed carbon films on the filament post surface.
Unfortunately, this technique has an inherent tendency to produce high intrinsic stress in the thin film deposited on the electrodes 11. After repeated deposition cycles, the highly-stressed carbon film tends to accumulate on the electrodes. When the film reaches a critical thickness on the electrodes, the film tends to delaminate from the surfaces of the electrodes, which produces the unwanted carbon particles and carbon voids described above. Although this prior art design is workable, an improved solution for forming thin film overcoats that addresses the limitations of the prior art would be desirable.